The solid state of chemical compounds can be amorphous (i.e. no long-range order in the positions of atoms) or crystalline (i.e. atoms arranged in an orderly repeating pattern). The term “polymorph” refers to a particular crystal form (i.e. structure of crystal lattice) of a chemical compound that can exist in more than one crystal form in the solid state. Polymorphs can differ in such chemical and physical (i.e. physicochemical) properties as crystal shape, density, hardness, color, chemical stability, melting point, hygroscopicity, suspensibility, solubility and dissolution rate, and such biological properties as biological availability, biological efficacy and toxicity.
Predicting physicochemical properties such as melting point or solubility for a crystal form in which the solid state of a chemical compound can exist remains impossible. Furthermore, even predicting whether the solid state of a compound may be present in more than one crystal form is not possible.
PCT Patent Publication WO 2011/017342 discloses 1-[(2-chloro-5-thiazolyl)methyl]-3-(3,5-dichlorophenyl)-2-hydroxy-9-methyl-4-oxo-4H-pyrido [1,2-a]pyrimidinium inner salt and methods for its preparation, as well as the utility of this compound for controlling invertebrate pests. New solid forms of this compound, their compositions and methods of their preparation and use have now been discovered.